Question: I am trying to create a table that
will disallow a NULL value from being inserted into my table, based
upon a condition, using an if-then-else.
I know that I can easily disallow NULL values on insert with the
NOT NULL clause, but I want the value to change depending on the
value of another inserted column:
- If col1 is equal to 1 or 2, then ensure than col2 is
null
- If col2 is equal to 3 or 4 then ensure that col2 is NOT NULL
In sum, I want to create this complex business rule as a
conditional check constraint, using if-then-else logic to check for
complex Boolean expressions?
Answer: You can create complex
check constraints that implement conditional logic. Oracle guru
Laurent Schneider shows how to create a table constraint that
checks for NULL values based upon the values of other columns in the
INSERT statement:
The syntax for using the purge tablespace command is:
create table
test
(
col1
int not null,
col2 int default null,
constraint
chk_b
check((col2 is not null and col1 in(3,4)) or (col2 is null and col1
in (1,2)))
);
As we see, you can make check constraints quite complex and use
Boolean logic to enforce complex business rules at the database
level.
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